At present, polyphase voltage inverters are used to drive polyphase electrical loads. These electrical loads are for example reversible machines such as starter-alternators. The polyphase voltage inverter is a DC/AC converter. It is connected upstream to a DC supply source and connected downstream to the phase windings of the load. The inverter is supplied with power by the DC supply source. It is controlled in terms of pulse width modulation by a control logic.
The inverter comprises a number of bridge arms, each comprising for example two static switches equipped with free-wheel diodes, i.e. two levels. The mid-point of each pair of switches of one and the same bridge arm is connected to a phase winding of the load. The control logic makes it possible to control the switches of one and the same bridge arm so as to avoid short-circuiting the supply source, for example by controlling them in a complementary manner.
A number of techniques exist for controlling the polyphase inverter, in particular voltage control of the load or current control of the load. To stabilize the voltage, on the upstream side of the inverter, according to the known control techniques, the inverter comprises a decoupling capacitor upstream. This decoupling capacitor makes it possible to filter the current entering the inverter, said current being subject to considerable discontinuities. This decoupling capacitor has a high capacitance so as to keep the input voltage of the inverter constant and to avoid any oscillation effects. The physical size of the decoupling capacitor is very large. Such a decoupling capacitor poses size problems when used in a restricted space.
In order to reduce the physical size of the decoupling capacitor, use is currently being made of capacitors with a high volume capacitance, such as electrochemical capacitors. However, these capacitors exhibit a lack of reliability, particularly in high-temperature or humid environments.
Moreover, the manufacture of these decoupling capacitors requires the use of expensive technologies on account of the demanding specifications. This expensive technology increases the overall cost of the polyphase inverter.
The control techniques mentioned above therefore do not make it possible to stabilize the voltage of the upstream part of the inverter.